In recent years, digital radiation detecting apparatuses have been commercialized. The known digital radiation detecting apparatus includes a scintillator (phosphor) layer laminated on at least the surface of a photoelectric conversion element formed on a large-area plane. The scintillator layer emits light responsive to X-ray irradiation. As disclosed in U.S. Pat. No. 6,262,422, U.S. Pat. No. 6,278,118 and the like, a radiation detecting apparatus (also called a “direct deposition type” or a “direct type”) composed of a photodetector (also called a “sensor panel”) and a scintillator layer formed directly on the photodetector is known as an apparatus having a high sensitivity and a high sharpness among the digital radiation detecting apparatuses. The photodetector is composed of a photoelectric conversion element unit in which a plurality of electric elements such as photosensors and TFTs is two-dimensionally arranged. The scintillator layer is for converting radiation to light capable of being detected by the photoelectric conversion element.
As disclosed in U.S. Patent Application Publication No. 2002/17613 and the like, a radiation detecting apparatus (also called a “paste together type”, or “indirect type”) composed of a photodetector and a scintillator panel bonded together with the photodetector is known. The photodetector is composed of a photoelectric conversion element unit in which a plurality of electric elements such as photosensors and thin film transistors (TFTs) is two-dimensionally arranged. The scintillator panel is composed of a scintillator layer formed on a supporting substrate. The scintillator layer is for converting radiation to light capable of being detected by the photoelectric conversion element. As the scintillator layer, for example, a material containing CsI having a columnar crystal structure formed by evaporation as the principal component is known. In order to prevent the penetration of moisture from the outside into such a scintillator layer, it is practiced to form a scintillator protection layer. In particular, the CsI material is an absorbent material, and consequently a problem of deterioration of resolution caused by the absorption of moisture by the CsI material can easily occur.
U.S. Pat. No. 6,262,422 discloses the radiation detecting apparatus produced by preparing the photodetector by forming a protection layer on the surface of the photoelectric conversion element unit formed on the surface of a glass substrate, by forming the scintillator layer made of CsI having the columnar crystal structure directly on the surface of the protection layer by the evaporation method, and by forming a scintillator protection layer consisting of an organic thin film by the CVD method so as to cover the surfaces of the photodetector and the scintillator layer. Poly-para-xylylene is disclosed as a material of the organic thin film.
U.S. Pat. No. 6,278,118 discloses a radiation detecting apparatus produced by forming the scintillator layer made of CsI having the columnar crystal structure on the surface of the photodetector with a protection layer put between them by the evaporation method, and by forming a scintillator protection layer so as to cover the surfaces of the photodetector and the scintillator layer, and further by providing a covering resin making the periphery of the scintillator protection layer adhere closely to the surface of the photodetector.
U.S. Patent Application Publication No. 2002/017613A discloses a radiation detecting apparatus produced by pasting the scintillator panel together on the photodetector. The scintillator panel is formed on a supporting substrate made of a carbon substrate and then, sequentially, a reflective layer consisting of a reflective metal thin film, the scintillator layer formed on a supporting member arranging a scintillator foundation layer thereon by evaporation, and the scintillator protection layer consisting of an organic film (poly-para-xylylene) provided so as to cover the surface of the supporting member and the scintillator layer.
However, there is a case where an abnormal growth (splash) defect is generated in the scintillator layer, which has the columnar crystal structure formed by the evaporation and consists of alkali halide such as CsI:Na and CsI:Tl, at the time of the formation of the scintillator layer. In particular, in a radiation detecting apparatus for radiographing a human body, the thickness of the scintillator layer is needed to be 400 μm or more, and the abnormal growth parts sometimes become projections each having a diameter of 300 μm or more and a height of 20 μm or more in that case. Furthermore, there is a case where concave portions each having a depth of 20 μm or more in a doughnut shape are formed around each of the abnormal growth parts in the projections. The inventors found that the thickness of the scintillator protection layer was required to be 20 μm or more for covering the abnormal growth defect parts of the scintillator layer including such projections and concave portions to satisfy the need for moisture proofing. However, because the scintillator protection layer using the organic film made of poly-para-xylylene disclosed in the above-mentioned patent document is formed by the CVD method, the film formation speed of the scintillator protection layer is about 100 to 2000 angstroms/minute, which is slow, and the film formation time required for forming a 20 μm scintillator protection layer is correspondingly between 100 minutes and 2000 minutes. Consequently, the prior art has the problem that productivity is poor.
Moreover, when the scintillator protection layer consisting of an organic film made of poly-para-xylylene used for a large-area radiation detecting apparatus (for example, 43 cm×43 cm) such as an X-ray digital camera is formed as a film by the CVD method, the film thickness distribution in the surface of the scintillator protection layer becomes large. When the light emitted by the scintillator layer is reflected by a reflection film to enter the photoelectric conversion element in the radiation detecting apparatus like ones disclosed in the above-mentioned prior art documents 1 and 2, optical path lengths are different from one another owing to the film thickness distribution in the surface of the scintillator protection layer. As a result, the organic film has a problem that the resolution of the acquired image decreases. Moreover, in the radiation detecting apparatus like the above-mentioned prior art technical document 3, when the light emitted by the scintillator protection layer enters a light receiving element, differences are generated in optical path lengths by the film thickness distribution in the surface of the scintillator protection layer, and consequently this radiation detecting apparatus also has the problem that the resolution of the acquired image decreases.
Moreover, the organic film made of poly-para-xylylene has the following problems. First, the organic film does not adhere well with the protection layers of the patent documents 1 and 2 and the scintillator foundation layer of the patent document 3, and exfoliation or a gap is generated at the interface between the scintillator protection layer and the protection layer, or the interface between the scintillator protection layer and the scintillator foundation layer. Consequently, the organic film suffers from the problem that the moisture resistance and the shock resistance are both lower at the interface between the scintillator protection layer and the protection layer, and at the interface between the scintillator protection layer and the scintillator foundation layer. Moreover, although the prior art disclosed in the patent documents 1 and 2 secures the moisture resistance and the shock resistance by providing a covering resin at the ends of the scintillator protection layer end, this also has the problem that the configuration may increase in cost.